surface tension

SURFACE TENSION

Outer layer of liquid molecules on the surface do not experience any interaction from above

Caused by attracting forces between the molecules at the surface

EFFECTS OF SURFACE TENSION

Several effects of surface tension can be seen with ordinary water:Several effects of

surface tension can be seen with ordinary water:

Several effects of surface tension can be seen with ordinary water:A. Beading of rain water on

a waxy surface, such as a leaf. Water adheres weakly to wax and strongly to itself, so water clusters into drops.

B. Formation of drops occurs when a mass of liquid is stretched.

water adhering to the faucet gaining mass until it is stretched to a point where the surface tension can no longer bind it to the faucet. It then separates and surface tension forms the drop into a sphere. If a stream of water was running from the faucet, the stream would break up into drops during its fall. Gravity stretches the stream, then surface tension pinches it into spheres.

C. Flotation of objects denser than water occurs when the object is nonwettable and its weight is small enough to be borne by the forces arising from surface tension.

D. Separation of oil and water (in this case, water and liquid wax) is caused by a tension in the surface between dissimilar liquids.

E. Tears of wine is the formation of drops and rivulets on the side of a glass containing an alcoholic beverage. Its cause is a complex interaction between the differing surface tensions of water and ethanol; it is induced by a combination of surface tension modification of water by ethanol together with ethanol evaporating faster than water.

SURFCANTS

Surface tension is visible in other common phenomena, especially when surfactants are used to decrease it:

Soap bubbles have very large surface areas with very little mass. Bubbles in pure water are unstable. The addition of surfactants, however, can have a stabilizing effect on the bubbles

Notice that surfactants actually reduce the surface tension of water by a factor of three or more.

Emulsions are a type of solution in which surface tension plays a role. Tiny fragments of oil suspended in pure water will spontaneously assemble themselves into much larger masses. But the presence of a surfactant provides a decrease in surface tension, which permits stability of minute droplets of oil in the bulk of water (or vice versa).